Energy gap for infinite system using segment DMRG?
Posted: 11 Apr 2021, 18:18
Hi everyone,
Currently, given a system, there are two ways of extracting an energy gap: either by doing finite DMRG (downside: there are boundary effects) or by doing periodic systems (downside: this is very costly since if naively requires the square of the original bond dimension).
Ideally, there is a third option, which avoids the above two downsides: one obtains the ground state on an infinitely-long system and one then uses segment DMRG to keep the left-infinite and right-infinite environments fixed, and then finds an orthogonal state where one only optimizes a finite number of sites in between these fixed environments.
My question: is this possible using the current package, or does this something we still need to implement? My confusion: it seems that MPS, MPOs and DMRG all allow for the 'segment' option (according to the documentation), but it is unclear to me at which point one actually feeds in the knowledge of the infinite left and right environments (which are of course crucial for correctly calculating the energy when doing DMRG).
With best wishes,
Ruben
Currently, given a system, there are two ways of extracting an energy gap: either by doing finite DMRG (downside: there are boundary effects) or by doing periodic systems (downside: this is very costly since if naively requires the square of the original bond dimension).
Ideally, there is a third option, which avoids the above two downsides: one obtains the ground state on an infinitely-long system and one then uses segment DMRG to keep the left-infinite and right-infinite environments fixed, and then finds an orthogonal state where one only optimizes a finite number of sites in between these fixed environments.
My question: is this possible using the current package, or does this something we still need to implement? My confusion: it seems that MPS, MPOs and DMRG all allow for the 'segment' option (according to the documentation), but it is unclear to me at which point one actually feeds in the knowledge of the infinite left and right environments (which are of course crucial for correctly calculating the energy when doing DMRG).
With best wishes,
Ruben